This application claims priority from German Patent Application No. 101 55 620.9-53, filed Nov. 13, 2001, and entitled CIRCUIT DEVICE HAVING A CENTRAL FUSE.
The invention relates to a circuit device, and in particular, to a semiconductor memory device having a fuse.
Fuse boxes have widely been used to activate redundancies on chips or integrated circuits, mostly for memory design. Specifically, redundancies have been used in DRAM design since the 256 k generation to improve yield and profitability. In redundancy, spare elements such as rows and columns are used as logical substitutes for defective elements. The substitution is commonly controlled by a physical encoding scheme. As memory density and size increase, redundancy continues to gain importance. Modern DRAM designs typically employ both row and column redundancy concept. Thus, memory fault repair is a reconfiguration of the memory circuit that inhibits the use of faulty circuit elements and enables the use of operating spare (redundant) elements. Circuit elements, which are repaired in a memory, include rows, columns, blocks (clusters), subarrays and arrays of memory cells.
The repair procedure typically consists of three phases: (1) detection and location of faulty (defect) elements, (2) assignment of operating spare (redundant) elements, and (3) disconnection of the faulty elements and integration of the assigned redundant elements with the memory operation.
Disconnection of faulty elements and engagement of spare elements may be implemented externally by laser, fuse and antifuse programming or by on-chip repair circuit applying electrical fuse, antifuse, EPROM, EEPROM, FRAM, SRAM or other by stable programmable circuit elements which, in the following, are simply referred to as fuse elements. These fuse elements are provided in a fuse box (or fuse repository) which is able to activate the redundant circuit elements provided as spare elements in the circuit to be repaired.
Besides the application of fuse boxes in defect repairable circuit designs, it is also possible to use fuse boxes in electrical circuit modules which contain adjustable circuit elements which can be adjusted by an appropriate programming of the fuse elements contained in the fuse box. For example, fuse boxes could also be employed in analogue circuits for trimming purposes; wherein adjustable circuit elements are adjusted such that the circuit meets predetermined circuit specifications.
In commonly known modern circuit devices, such as semiconductor memories, each individual semiconductor circuit is provided with a local fuse box connected thereto. This fuse box serves the associated circuit in that it enables the activation of adjustable circuit elements therein. If a semiconductor memory chip, for example, contains six memory circuits thereon, then at least six separate local fuse boxes connected to these memory circuits are commonly provided.
Integrated logic and, particularly, memory circuits are constantly miniaturized in order to constantly increase the memory density per unit chip area. Employing fuse box layout concepts, however, requires additional chip area since the commonly used laser programmable fuse elements have minimum sizes defined by the laser programming process. Consequently, there exists a trade-off between memory density and yield improvement when using fuse box concepts.
In view of these drawbacks encountered in the prior art, the problem to be solved by the invention is to provide a circuit device, in particular a semiconductor memory device, which employs a fuse box concept having programmable fuse elements adapted to adjust adjustable elements, which consumes less chip area.
According to one aspect of the invention, a semiconductor memory device includes a plurality of integrated circuit modules each having a plurality of module elements and at least one adjustable module element. At least one fuse box is electrically connected to the plurality of integrated circuit modules. The fuse box has a plurality of programmable fuse elements, that, when programmed, adjust the adjustable module element.
Thus, the at least one fuse box or fuse repository (which can contain several fuse boxes and which can be partitioned in the layout to have several fuse box blocks) is associated with a plurality of integrated circuit modules. The integrated circuit modules have to be understood as independent integrated circuits, i.e., autonomous integrated circuits, such as different memory circuits on a semiconductor memory chip. Therefore, the term integrated circuit modules refers to independent integrated circuits on a chip and not to parts of a single integrated circuit on this chip.
According to another aspect of the invention, several of the independent integrated circuit modules are connected to a single fuse box or fuse repository, which constitutes a central fuse box of the circuit device. This central fuse box serves different integrated circuit modules by enabling an adjustability of the integrated circuit modules by adjusting the adjustable module elements thereof. This is achieved by a suitable programming of the fuse elements of the fuse box.
Preferably, all components of the at least one fuse box are clustered or grouped in one designated region within the circuit device, e.g., a designated region of the chip. In particular, the programmable (or adjustable) fuse elements of the fuse box are concentrated in a designated fuse element area. In case that laser-programmable fuse elements are used within the fuse box, such clustering or grouping of the programmable fuse elements greatly facilitates the positioning and programming of the laser-programmable fuse elements by the laser programming tool.
In the prior art, local fuse boxes have been widely employed in circuit devices. These local fuse boxes only serve adjacent or close by integrated circuits and are not adapted to configure adjustable module elements, for example, the whole chip. In contrast to the prior art, the control logic provided within the fuse box according to the invention does not linearly increase in its complexity when the number of programmable fuse elements is increased. The inventive (centralized) fuse box requires less chip area compared to several local fuse boxes. This will lead to a considerable reduction of production costs.
According to a preferred embodiment, the number of the programmable fuse elements is not sufficient to adjust all of the adjustable module elements of all of the integrated circuit modules. Thus, the invention proposes to intentionally select the number of programmable fuse elements such that it does not allow to configure all of the adjustable module elements of all of the integrated circuit modules simultaneously. Instead, the number of the programmable fuse elements is only sufficient to adjust a fraction of the adjustable module elements. For example, the number of the programmable fuse elements could be selected such that only up to 90%, preferably only up to 75% and even more preferably only up to 50% of the adjustable module elements of all the integrated circuit modules could be adjusted therewith.
Surprisingly, this substantial reduction of the number of the programmable fuse elements does not greatly affect the overall yield in the production of circuit devices according to the invention. This is essentially due to the fact that in many applications only adjustable module elements in a specific region of the circuit device need to be adjusted. If, for example, the adjustable module element is a redundant module element adapted to replace a defect module element, then only the redundant module elements in certain areas of the circuit device need to be activated. In this context, it has to be borne in mind that defects (defect module elements) in circuit devices are very often clustered leading to fault-free circuit device areas and faulty circuit device areas.
Since one aspect of the invention provides a circuit device with a centralized fuse box, it is very often possible to activate all necessary redundant module elements in order to replace defect module elements in circuit device areas, where defect clustering occurs. Therefore, even though the number of the programmable fuse elements is considerably reduced compared to conventional circuit devices with fuse boxes, it is in many cases nevertheless possible to configure all necessary adjustable module elements even with this reduced number of programmable fuse elements. Only in cases, when a xe2x80x9cworst case scenarioxe2x80x9d is encountered, i.e., in cases where all of the adjustable module elements of all of the integrated circuit modules need to be adjusted, this number of the programmable fuse elements is not sufficient. This drawback, however, only rarely occurs and is more than compensated by the great benefit of a considerably reduced chip area consumption of the fuse box.
According to another preferred embodiment, the integrated circuit modules are defect repairable circuit modules and the adjustable module element is a redundant module element adapted to replace a defect module element. As stated previously, a major application of fuse box concepts resides in the configuration of defect repairable circuits. In this case, the fuse elements of the fuse box can be used to configure or adjust a redundant module element in such a way, that it electrically replaces a defect module element. Thus, for example production faults occurring within the production of the circuit device can be repaired to a certain degree.
The defect repairable circuit modules could be defect repairable memories and the redundant module element could be a redundant memory element. The described inventive concept of using a centralized fuse box is particularly suited for defect repairable memory concepts for example in DRAM designs.
According to a preferred embodiment, the fuse elements comprise volatile and/or non-volatile memories, particularly laser-programmable fuse elements and/or electrically programmable fuse elements. Typically, the programmable fuse elements used in fuse boxes are laser-programmable fuse elements which can be programmed by cutting a fuse link by a focused laser beam. However, also electrically-blowable fuse elements have been widely used. The invention is also applicable to all other kinds of fuse elements as long as they are bistable elements. For example, the fuse elements could also be some sort of volatile and/or other non-volatile memories. Also, the fuse box comprising the programmable fuse elements could be connected to another fuse box of a higher hierarchy, which is adapted to control the state of the fuse box in the lower hierarchy circuit device. A hierarchical fuse box concept could be obtained in this way.
According to another embodiment, the fuse box is formed on a separate fuse chip or a separate fuse board or MCM. For example, a special fuse chip could be designed and optimized which only contains fuse boxes. The production process for the designated fuse chip would in this case not suffer from any constraints which might arise if this production process also has to be applied to a semiconductor memory chip.
According to another preferred embodiment, the fuse box comprises at least one fuse box register connected to the fuse elements for storing fuse data. The fuse box register can be designed as a shadow register, the register element of which are connected in parallel to associated fuse elements. Thus, preferably each register element is exactly connected in a 1:1 mapping to exactly one fuse element. Furthermore, the fuse box register preferably comprises a register input and a register output for serially shifting fuse data in and out of the fuse box register.
According to another preferred embodiment the fuse box controller of the fuse box is adapted to detect upload and/or download errors of data uploaded/downloaded into/from the fuse box. For example, fuse data could initially be stored in a plurality of fuse elements. In an initializing step, the fuse elements are read out and its contents are stored in fuse box register elements of a fuse box register. From the fuse box register the data could be downloaded to integrated circuit modules containing adjustable module elements. If a data transmission error occurs during the download from the fuse box to the integrated circuit modules, the fuse box controller could set an error flag. Similarly, if an error occurs upon uploading of data from the integrated circuit modules to the fuse box, transmission faults could also be indicated.
According to another preferred embodiment the fuse box comprises a bi-directional input/output pin for inputting and/or outputting fuse data. This bi-directional input/output pin allows a serial transferal of data to and from the fuse box. For example, fuse data could be outputted to some external testing tool in order to analyze faults of a defect repairable memory.
According to a particularly preferred embodiment of the invention, the at least one fuse box and the integrated circuit modules are serially connected in a daisy chain arrangement. Compared to a parallel connection scheme of the circuit modules and the fuse box in for example a tree- or star-like architecture, the serial daisy chain arrangement requires less wires to be routed across the chip. Thus, the daisy chain arrangement implies that at least one wire serially passes through the integrated circuit modules and the fuse box so that not every integrated circuit module is directly connected to the fuse box by a (parallel) wire.
According to another preferred embodiment of the invention, the fuse box comprises a fuse box controller enabling serial shift operations of data through the daisy chain arrangement. Preferably, the data stored in the fuse elements of the fuse box is first read out into a fuse box register. Subsequently, the data is serially shifted out from the fuse box register to the integrated circuit modules in order to adjust the adjustable module elements.
Preferably, the fuse box has a fuse data input and a fuse data output connected to opposite ends of the chain of serially connected integrated circuit modules, respectively. Accordingly, the daisy chain of serially connected integrated circuit modules is connected to input/output terminals of the fuse box at opposite ends to form a closed loop. Preferably, data can be serially shifted from the fuse box to the integrated circuit modules (download operation) or serially shifted from the integrated circuit modules back to the (central) fuse box (upload operation). Preferably, a fuse box controller of the fuse box enables uploading of data from the integrated circuit modules to the fuse box. The uploading operation can thus be easily controlled by the fuse box controller of the fuse box.
Preferably, the fuse box controller is adapted to program at least one of the fuse elements based on an analysis of the uploaded data in order to adjust and/or readjust at least one of the integrated circuit modules. Thus, in this particularly preferred embodiment, several fuse sessions/fuse passes are possible. For example, during a first and initial fuse pass, fuse data is downloaded from the fuse box (e.g., from the fuse box register) to the integrated circuit modules. This first download operation of fuse data to the integrated circuit modules could for example activate a first set of adjustable module elements in a desired manner. If, in a later testing or operational stage of the circuit device, a further necessity of adjusting or readjusting some or all of the integrated circuit modules arises, then a second fuse pass (second fuse session) might be performed. In this case, the data of the adjustable module elements, for example of redundancy registers of defect repairable memories, are uploaded into the fuse box (e.g., into a fuse box register in the fuse box). The fuse box controller is preferably adapted to determine the differences between the original fuse data and new data e.g., from a subsequently performed test run in order to program new fuse elements in the next fuse session. Furthermore, the fuse box is preferably adapted to identify additionally programmed registers in the integrated circuit modules by other tools. After identifying (by comparing fuse content and integrated circuit module content) the appropriate signals/data are uploaded into the fuse box to start a further (second, third, . . . ) burn session.
According to a preferred embodiment, the fuse box and the integrated circuit modules are connected by one bi-directional data line and at least two control lines. Preferably, the control lines control the handover mechanism of the data upload/download from/to the integrated circuit modules to the (centralized) fuse box. As a bi-directional data line is used for transmitting data between the integrated circuit modules and the central fuse box, fewer wires then in comparable parallel wiring concepts are necessary which implies that less chip area is consumed by wiring.
According to another preferred embodiment, the fuse box contains a plurality of data fuse elements and a plurality of control fuse elements, the control fuse elements being adapted to control at least one multiplexer of at least one of the integrated circuit modules in order to configure the daisy chain arrangement. Thus, a first level of fuse elements is provided in the fuse box for storing fuse data needed for adjusting the adjustable module elements of the integrated circuit modules. Additionally, a second level of fuses referred to as control fuse elements is provided in order to configure the at least one multiplexer. By programming the control fuse elements, it is possible to control the multiplexer such that one or more of the integrated circuit modules are for example bypassed by the daisy chain.
Preferably, at least one of the circuit modules comprises two multiplexers connected by a bypass line and, in a bypass stage of the multiplexers, the bypass line forms part of the daisy chain so that at least a part of the adjustable circuit module is bypassed by the daisy chain. Preferably, the multiplexers are disposed at the input and output of the integrated circuit module, respectively. In a bypass state of the multiplexers, incoming data is routed by the input multiplexer into the bypass line and through the output multiplexer out of the integrated circuit module. Consequently, at least a part of the integrated circuit module is bypassed and is no longer part of the daisy chain arrangement. Accordingly, the controllable multiplexers allow a specific xe2x80x9caddressingxe2x80x9d of integrated circuit modules by fuse data sent from the fuse box.
According to another preferred embodiment, the fuse box controller is adapted to form a formatted bit stream of fuse data to be inputted into and/or outputted from the fuse elements, the bit stream comprising for each adjustable circuit module at least one adjustment control bit and, if the adjustment control bit is set, a plurality of data bits. It has to be understood that inputting/outputting of fuse data into or out from the fuse elements could also imply inputting/outputting of data into register elements of a fuse box register. Preferably, the fuse box controller is adapted to compress/decompress data outputted to the integrated circuit modules and/or compress data inputted from the integrated circuit modules into the fuse box. Preferably, the formatted bit stream can directly be used for a programming operation of the fuse elements without any further (external) signal processing of the fuse data.
Preferably, the data bits represent address value data bits of a defect circuit element to be replaced by the redundant circuit element associated with the adjustment control bit. Consequently, in case the adjustment control bit is set, the following data will be considered as address value bits of a defect circuit element. Conversely, if the adjustment control bit is not set, dummy data bits could be generated and outputted by the fuse box controller to the integrated circuit modules. Therefore, in case an adjustable module element does not need to be adjusted by programming of associated fuse elements, it is not necessary to designate fuse elements for data bits representing address value data bits for this adjustable module element. Instead, preferably only a single adjustment control bit is deactivated (for example set to logic 0) in order to indicate that the adjustable module element does not need to be adjusted. In this case, no further fuse elements need to he associated with this adjustable module element. This effectively results in a data compression/decompression of data inputted/outputted to/from the fuse elements. This in turn results in an increased number of adjustable module elements which can be adjusted by a given number of fuse elements. Conversely, for a given number of adjustable module elements which should be simultaneously adjustable, less fuse elements need to be provided within the centralized fuse box.
Preferably, the fuse data comprise at least one length controlled bit indicating the number of following data bits. In case the centralized fuse box is used in a complex system of different integrated circuit modules having different address lengths, a formatted bit stream having a length control bit could be used wherein the length control bit indicates the number of following data bits (for example address length bits). Therefore, it is not necessary to associate all integrated circuit modules with the maximum number of fuse elements needed by a single integrated circuit module. Instead, the number of fuse elements associated with individual integrated circuits modules can be controlled independently.
In the following, the invention will be described by way of examples with reference to preferred embodiments shown in accompanying drawings. These preferred embodiments all refer to defect repairable memories having redundant memory elements which can be activated by programming associated fuses. However, it has to be understood that the invention is not restricted to such applications.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.